ONLINE BRUSSELS HERITAGE - ONE-DAY SEMINAR - 11/12/2014

is not necessarily trained in thermal insulation techniques.

Double-glazing can often be fitted into an existing window frame using a technique whereby the glazing rebate is widened. The width of the rebate, after milling, determines the performance of the glazing that will be fitted. In effect, the U-value, or heat transmission coefficient of the glass, is linked to the thickness of the air or gas space separating the two panes. By way of example, to obtain a U-value of 1.1 W/m².K, the thickness of the double-glazing inter-layer should be 15 or 16 mm. Given the cross-sectional profiles of old wooden window frames, it is not always possible to fit glass of such thickness. Double-glazing with 12 mm or even 9 mm interlayers will therefore often be chosen. Another method is to fit single-glazing but with a low emissivity layer. This consists of laminated glass fitted with a low emissivity layer that reduces the heat transmission coefficient of the single-glazing to a U-value of around 3.2 W/m².K. As a reminder, normal single-glazing has a U-value of 5.8 W/m².K. This technique therefore offers a substantial improvement even if it is not comparable to the performance of contemporary double-glazing. In the case of heritage buildings this type of glazing is interesting, particularly when the glass in sash window frames is being replaced. This avoids having to install double-glazing with fake sash bars. This glazing is available in drawn and blown glass versions for the external face.

The thermal efficiency of front doors can be enhanced by fitting seals. In the case of doors adhesive seals are generally used, while for window frames the best solution is fitting seals in a groove made using a router. This is not recommended for doors as the door frame could be weakened. A brush seal can also be fitted to the bottom of the door to improve its performance. An old door cannot, of course, be brought up to level of performance of a new one, but a significant improvement can be made.

Craftspeople face limits in terms of improving thermal efficiency and I think that these limits should be examined. A desire to ensure the continued existence of trades that enable existing elements to be maintained and preserved risks leading us into a dead end. Indeed, it should be borne in mind that, by dint of encouraging very high levels of efficiency, a point will be reached where the only choice possible will be to replace, especially in terms of exterior joinery. A quick examination of Batex projects shows, with some notable exceptions, that almost every one includes the replacement of window frames. Questions therefore need to be asked about the level that we want to achieve. As part of the reflections underway on reorienting the system of renovation and energy grants, it would perhaps be good to consider greater progressivity in the thresholds. If we take, for example, the fitting of double-glazing in an existing frame, the maximum U-value required for the energy grant is 1.2 W/m².K (this requirement is not appropriate for the renovation grant). In a sizeable number of cases, this level of efficiency will not be achieved and individuals could be discouraged. They will therefore opt for the “easy solution” and replace everything. As regards low emissivity single-glazing, it is automatically excluded as it has a U-value of 3.2 W/m².K. Double-glazing is subsidised for the purpose of the energy grant but is not eligible for a renovation grant. Why not consider making it eligible? In the case of wall insulation, grants also encourage high levels of efficiency that rule out the insulating renders applied for the purpose of thermal correction referred to by Julien Bigorgne from Apur (see p. 24-34).

TRAINING PROFESSIONALS AND EDUCATING INDIVIDUALS

For several years now, numerous courses on the theme of sustainable renovation have been offered to professionals by actors such as Brussels Environment, the Belgian Building Research Institute (BBRI) and the Construction Reference Centre (CDR). From these many initiatives, I want to highlight the “Interactive technical course on window frames” organised by the CDR and 21 Solutions. This is a course that focuses on both requirements in terms of energy performance and constraints in terms of heritage. It includes on-site visits, a diagnostic approach and encourages a very open-minded consideration of the range of technical solutions available, according to the energy renovation scenarios chosen.

The role of the Centre Urbain's information desk, situated at Halles Saint-Gery, is to inform individuals about all aspects of housing renovation. We don't do this work alone, of course. There are also the associations that are part of the Habitat network, as well as other actors. We have been around for 25 years and our special feature is our cross-disciplinary approach. We approach housing from the perspective of different themes-energy, building pathology, heritage, acoustics, planning - by establishing bridges between all

114 | Sustainable renovation of a Brussels house: a challenge for building tradesmen